This invention relates to a probe terminal for installation in an enamelled apparatus, which is suitable for measuring the internal temperature of the apparatus and for detecting any damage to the enamelled lining. The term "apparatus" as used hereinafter denotes an internally enamelled reactor, container, vessel or the like, which is generally of steel construction. Such enamelled apparatus are used generally for processing highly corrosive liquids, suspensions and sludges, which are indicated hereinafter by the term "liquids" for simplicity.
The term "probe", as used hereinafter, indicates any element which can support the terminal of the present invention. A thermometer sheath, a baffle, a valve head, or the like, can be used as "probe".
In enamelled apparatus used in the chemical industry, temperature is measured by a thermocouple or a resistance thermometer (e.g. a Pt 100, i.e. a platinum wire which has a resistance of 100 ohms at 0.degree. C.) inserted into a probe and connected at its top end to the temperature measurement and alarm instrument, which gives an alarm whenever the temperature exceeds the set limit.
The following are used for measuring temperature by conventional methods:
(a) an enamelled steel probe fitted with a terminal constructed entirely of tantalum and screwed into the lower end of the probe by way of a TEFLON (PTFE) seal gasket. Said terminal comprises a lower cylindrical end abutting from the terminal, which houses the thermocouple junction generally immersed in oil; PA0 (b) a completely enamelled steel probe in which the thermocouple conductors are inside the probe, in which lower end is inserted the thermocouple junction generally immersed in oil.
Obviously a Pt 100 resistance thermometer or any other suitable thermometer, e.g. a mercury thermometer, can be used instead of a thermocouple.
When temperature is measured by method (a), there is rapid response to sudden temperature variations, and a greater sensitivity than method (b), in which the enamel layer acts as a heat insulant, and considerably slows down the heat flow.
Further in regard of method (a) it must be added that tantalum or gold-platinum have to be covered with expensive corrosion resistant metal when positioned into a heated agitator type reaction vessel, thus we note increasing the time lag of the response. See German Pat. No. 1.648.227, column 1.
However, measurement by method (b) obviates the corrosion problems and dangers of incrustation which can arise when using a tantalum terminal. In German Pat. Nos. 1648277 and 2123371, the thermocouple or resistance thermometer wires are fitted on the outside of the probe between one layer of enamel and another. However, the methods of said patents require the entire probe to be replaced when the thermo-sensitive element is damaged.